1. Field of the Invention
The present invention relates to a new type of prosthesis foot, i.e. an artificial substitute for a lost biological foot.
2. Description of the Prior Art
The major problem which the invention is intended to solve is to provide a light-weight prosthesis foot which to the greatest possible extent resembles the biological foot concerning possibilities of movement and pattern of movement, effect of forces and loss of energy on walking, shape and appearence, etc., and which is also comparatively easy and cheap to manufacture and can easily be adjusted to different patients.
This problem has proven to be extremely difficult to solve, and although the patent literature comprises an immense number of proposals for solving the problem the presently available prosthesis feet leave much to be desired.
In the most common design of prosthesis feet there is provided a wooden core, to which an adapter for a lower leg prosthesis is attached. In these prosthesis feet separate elastic elements are used for achieving the desired simulation of the joints and the pattern of movement of the biological foot when walking, especially the desired mobility in the ankle joint, the spring joints (e.g. subtalar joint) and the toe area on the heal strike and the push-off. Such constructions, having a comparatively heavy core and separate foot joint mechanisms, are complex and heavy and cause considerable losses of energy on walking (the leg/leg prosthesis forms a long lever with the prosthesis foot at one end thereof). These and other drawbacks would remain even if one would choose a different material than wood as the core material in combination with the separate elastic elements/foot joint mechanisms.
Swedish Pat. No. 139,076 and German Pat. No. 354,246 can be mentioned as examples of prior art prosthesis feet based on a heavy wooden core and having the above mentioned drawbacks. The first mentioned patent disclosed a prostesis foot consisting of a heal and mid-foot portion, which is connected to a toe piece by means of a pair of cooperating plate springs, pressing the toe piece downwards. The heal portion is connected to a lower leg prosthesis in conventional manner by means of a ball joint and a rubber cushion. The latter patent discloses a different type of prosthesis foot--a so-called SACH-foot (Soft Ankle Cushion Heal) prosthesis--wherein a wedge shaped wooden lower leg prosthesis is connected to the prosthesis foot between a wooden toe and mid-foot piece and a heal cushion of rubber, a plate spring being connected between the front foot portion and the rear part of the lower leg prosthesis for providing resilient resistance to downwards/backwards motion of the lower leg prosthesis.
Russian Pat. No. 738,618 discloses an artifical foot comprising a moulded hollow heal and mid-foot piece, which is hingedly joined to a hollow toe piece. This artifical foot has most complex, heavy and expensive mechanisms for joining the foot to the lower leg prosthesis and providing the desired motions. For example, there are multiple connections between the artificial foot and the leg prosthesis, including a multitude of separate connection elements, such as a talocrural shock absorber with two telescoping sockets, a ball joint, a front shock absorber, double rear shock absorbers, rotation units, etc.